1. Field of the Invention
The invention relates to pipe leak detection and location systems and methods. Exemplary applications are suitable for leak detection and location in oil, natural gas and other pipelines that transport gaseous or liquid fluids over long geographic distances.
2. Description of the Prior Art
In order to implement environmental, health and safety policies, pipeline owners and operators monitor pipelines for leaks. When a leak is identified, the leaking pipe segment must be located, isolated and repaired as quickly as possible, so as to minimize loss of material and potential environmental infiltration. Often pipelines are routed through remote geographic areas or buried underground or beneath waterways, making external visual inspection difficult or impossible. In the past various remote leak detection and location methods have been employed to satisfy pipeline monitoring needs.
As shown in FIGS. 1A-1C, when pipes 10 experience a leak 12, the leak event causes upstream and downstream pressure wave disturbances 14 that propagate at the fluid's sound velocity C, also notated as Vs in technical literature. The pressure wave disturbance 14 is caused by sudden loss of pressure at the leak site, and travels upstream and downstream. As a pressure wave propagates through a given fluid volume, it alters the fluid's local density, thus modifying as a function of time the local sound velocity as well as the fluid flow velocity Vf.
The assignee of the present application and its predecessor companies have developed, patented and sold leak monitoring and detection systems utilizing ultrasonic flow meters oriented at selected monitoring locations (“Loc”) along a pipeline. As shown and described in U.S. Pat. Nos. 5,548,530 and 6,442,999, the entire contents of each being incorporated herein by reference, ultrasonic meters at each location periodically monitor, measure and record sound velocity C with a time stamp that is forwarded to a central station controller. The time clock at each location is periodically synchronized in cooperation with the controller, so that C measurements at each location can be compared and analyzed by the controller with a common time reference line. As a leak pressure wave disturbance anomaly propagates through the pipeline, upstream and downstream monitoring locations will experience localized variations in C caused by the disturbance at different times generally correlating to distance L from the disturbance. The controller identifies monitoring locations bracketing each side of the leak and then extrapolates the leak location based at least in part on difference in time between when each of the monitoring locations identified the leak event causation of sound velocity C change.
As noted in U.S. Pat. Nos. 5,548,530 and 6,442,999, ultrasonic flow meters are non-intrusive and do not have to be installed inside a pipe, as must be done with intrusive pressure transducers or mechanical flow rate transducers, such as in U.S. Pat. No. 5,272,646. Non-intrusive metering does not require pipe wall penetration, preserving pipe integrity, and lowering initial or retrofit installation costs.
Generally the ultrasonic flow meter leak detection and location methods and systems shown in U.S. Pat. Nos. 5,548,530 and 6,442,999 enable rapid identification and location of leaks within several hundred feet (100 meters) of location error between monitoring locations spanning distances of up to approximately 50 miles (75 kilometers). However in some applications leak identification and location solely based on monitoring change in sound velocity C is difficult because of the leak propagation disturbance wave attenuation, as shown in FIGS. 1A-1C.
In FIG. 1A, pipe 10 discharges into an atmospheric pressure tank 16. The localized line pressure at LocB is too low for strong propagation of the leak wave 14, so that there may be an insignificantly measurable variation in sound velocity CB. Thus, while LocA may measure a sound velocity variation CA, the location of the leak 12 between LocA and LocB is not as reliably extrapolated within a low desired error probability as can be done between monitoring locations having higher localized pressures.
In FIG. 1B the relative distance between leak 12 and monitoring location LocD is very large. Leak disturbance wave 14 propagation attenuation makes it more difficult to identify a leak event at LocD, especially for fluids having low density, e.g., low pressure gas transmission. A practical solution may be to reduce the distance between monitoring locations at the cost of additional meter installations, maintenance and monitoring. It is desirable to maximize rather than reduce distance between monitoring locations.
FIG. 1C is another exemplary challenge to accurate sound velocity monitoring in lower density or pressure fluids. In FIG. 1C pipeline 10 is serially transporting a relatively high density FLUID 1 ahead of an upstream lower density FLUID 2, with a known buffer fluid separating the two fluid streams. Leak 12 erupts within the FLUID 1 stream and generates leak propagation disturbance 14, monitored and identified at LocF as a change in CF. However, the upstream propagation wave 14 detected as a change in CE at LocE is traveling through less dense FLUID 2. Depending on the degree of upstream leak disturbance attenuation, it may be more difficult to identify that leak disturbance event at LocE, and differences in transmission propagation speed in FLUID 2 compared to FLUID 1 will make it more difficult to extrapolate to desired accuracy the location of leak 12 at the proper distances LE and LF.
Leak disturbances also alter localized flow velocity Vf, generally increasing upstream velocity and lowering downstream velocity, due to lower pumping resistance at the leak site. In U.S. Pat. No. 5,272,646 it is stated that both pressure and flow rate through an invasive differential pressure meter can be monitored at plural locations to locate a pipeline leak. It also has been observed by the present inventors that localized flow velocity Vf changes caused by leak pressure wave disturbances are identifiable when localized pressure at a measurement location is low or at greater distances from the leak location, compared to what can be identified by change in sound velocity C alone. They have noted that monitoring of both change in sound velocity and fluid flow velocity increased leak identification and location confidence. The leak disturbance may be identified by change in sound velocity or change in flow velocity. Contemporaneous identification and corroboration by both measurement modalities greatly increases identification and location confidence. However, known flow velocity meters require intrusion into the pipe.
Thus, a need exists in the art for a pipe leak detection and location system and method that utilizes non-intrusive instrumentation located outside of the pipe.
Another need exists in the art for a pipe leak detection system and method that monitors changes in fluid flow and sonic velocities, at plural locations in the pipe, and that associates changes in either with a leak event between two of the monitored locations.
Yet another need exists in the art for a pipe leak detection and location system and method that monitors changes in fluid flow and sonic velocities, at plural locations in the pipe that associates changes in either with a leak event between two of the monitored locations and further enables precise leak location identification.